1. Field of the Invention
The present invention concerns a cathodic arc deposition system used for coating, for example, an abrasion resistant film composed of TiN or the like onto the surface of tool steels.
2. Description of the Prior Art
A cathodic arc deposition system (also referred to as a vacuum arc ion plating system) is adapted to deposit an ionized film-forming material onto the surface of a substrate applied with a negative bias voltage by evaporating the film-forming material from an evaporation surface of a cathode comprising the film-forming material by means of arc discharge and ionizing the material, in a vacuum chamber.
In this case, since an arc spot is formed on the evaporation surface of the cathode by arc discharge, and the spot moves around at random during violent evaporation and ionization of the cathode material comprising the film-forming material, a shield is disposed for preventing the arc spot from shifting from the evaporation surface of the cathode to a non-evaporation surface (such as on the circumferential side of the cathode).
An apparatus having an arc evaporation source comprising a cathode or the like provided with a shield for preventing the shift of the arc spot and adapted to evaporate the cathode substance and deposit it on the surface of a substrate by utilizing the arc discharge is known, for example, as disclosed in Japanese patent Publication Sho 52-14690. FIG. 9 is an explanatory cross sectional view of the constitution of an arc evaporation source in a cathodic metal arc deposition system of the prior art.
In FIG. 9, a vacuum chamber wall 71 contains a cylindrical conductor 72 (having an axial line A) attached thereto by way of a ceramic insulator 73 and has an upper surface protruding into the chamber 71. An electroconductive cooling plate 74 which is internally cooled, is fixed to the upper surface of the conductor 72. Further, a disc-shaped cathode 75 is fixed to the upper surface of the cooling plate 74. The cooling plate 74 and the cathode 75 are disposed on the conductor 72 with each of their axial lines (center lines) being aligned with the axial line A.
The cathode 75 is made of a metal material for forming a film, and the upper surface thereof constitutes an evaporation surface 751. Numeral 76 denotes a cylindrical shield that surrounds the circumferential side of the cathode 75 with a gap G of about 2 to 3 mm, with the axial line thereof being aligned with the axial line A of the cathode 75. The shield 76 is fixed by way of an insulator 77 to the vacuum chamber wall 71.
The shield 76 is set such that the height of its upper edge 76a is identical with the height of the evaporation surface 751 before operation, for the reason to be described below. That is, if the upper edge 76a of the shield 76 is higher than the evaporation surface 751, evaporated metal is deposited on the shield 76 to fill the gap G, thereby causing transfer of the arc spot to the shield 76. On the other hand, if the upper edge 76a is lower than the evaporation surface 751, the arc spot may be formed at a portion not surrounded by the shield 76, to cause evaporation of the cathode metal in this portion and, as a result, the gap G is short-circuited to again transfer the arc spot to the shield 76.
As described above, it is necessary to keep the height identical between the upper edge of the shield and the evaporation surface of the cathode in order to stably maintain the arc discharge. However, as shown in FIG. 10 which illustrates the state of the cathode consumption when the operation is conducted for a long period of time, the evaporation surface 751 of the cathode 75 is consumed and retracted concavely into a configuration having a bottom and a wall, in which the upper surface 751a at the wall of the evaporation surface 751 is lower by a distance B shown in FIG. 10 than the upper edge 76a of the shield 76. Therefore, the evaporated cathode metal il deposited on the inner surface near the upper edge 76a of the shield 76 to fill the gap G, so that the shield 76 and the cathode 75 are short-circuited, and so that the arc spot transfers to the shield 76. Then, when the arc spot transfers to the shield 76, the cathode substance that fills the gap G is melted and evaporated by the arc to open the short-circuit between the shield 76 and the cathode 75, so that temporary arc interruption (stop of arc discharge) intermittently occurs frequently, making the arc discharge instable.
When arc disconnection occurs, a trigger electrode is actuated instantly to start the arc discharge again.